Assessing And Treating The Subtle Cavus Foot Deformity

Given the various conditions associated with the subtle cavus foot, it is important to be able to recognize the deformity in order to prevent related symptom recurrence and potential failure of surgical procedures. Accordingly, these authors present a guide to evaluation as well as conservative and surgical treatment options.

There has been much written about the adult flatfoot deformity in both the podiatric and orthopedic literature. On the other end of the spectrum, cavus foot or the “high arched” foot has received much less attention.¹ The common belief is that cavovarus feet are more often present in children.²

Cavus foot seems to be synonymous with neurological diseases. Neurological disease states such as poliomyelitis, Charcot-Marie-Tooth disease, Friedreich’s ataxia and cerebral palsy are common conditions that are paired with cavus foot deformity.³ This belief has led to a failure to recognize a more subtle type of cavus foot in adults, which is non-neurologic in nature.

The more subtle cavus foot is probably genetic and appears to be familial.⁴ When present in adults, it proves much more difficult to diagnose. The subtle cavus foot is non-neurologic and authors believe it to be biomechanically induced.⁵ This form of cavus deformity results from the first metatarsal position and hyperactivity of the peroneus longus muscle.

The subtle cavovarus foot has more recently been associated with lateral overload symptoms. Commonly associated conditions include ankle/rearfoot instability, peroneal tendon injury, lateral column pain and stress fractures of the lateral fourth and fifth metatarsals, tibia and fibula.^6,7 These are common clinical problems that the practicing podiatric physician encounters. Failure to recognize this deformity without correction potentially leads to a higher risk of recurrence of symptoms and failure of operative procedures.⁴

Key Tests To Evaluate The Subtle Cavus Foot
Johnson popularized the “too-many-toes” sign and made the once unrecognized condition of posterior tibial insufficiency commonplace.⁸ This popular sign was greatly responsible for many of the current advances in the treatment of this condition.⁹

The “peek-a-boo” heel sign initially surfaced in 1993 in an article about lower extremity contractures of the leg.⁹ In this publication, Manoli and colleagues described how this was a very sensitive test for identifying the subtle cavus foot deformity.

Patients perform the test with the feet aligned straight ahead. Normally, it is difficult to assess arch height objectively during a pedal physical examination. Often, patients will have an Achilles contracture that can cause external rotation. The patient must look down to make sure the feet lie straight ahead. When one views the feet from the front, the varus heel is visible. The heel “sticks out” medially or “peeks out” around the ankle, often referred to as the peek-a-boo heel sign. There can be false positives in two situations: when the patient has a very large heel pad and when there is a significant metatarsus adductus deformity.¹⁰

After identifying the heel varus, utilize the Coleman block test to determine subtalar joint flexibility or suppleness.¹¹ Perform the test by having the patient stand on a 1- or 2-inch wooden block. The first metatarsal always drops off the block medially. If the heel “corrects” to neutral, the rearfoot varus is flexible and caused or driven by the first metatarsal. The term for this is forefoot overdrive. However, if the heel remains in a varus position, where the first metatarsal drops medially, the subtalar joint is fixed in the varus position.   

The peroneus longus can also influence the position of the first ray. In order to differentiate its influence, place your thumb under the first metatarsal head and the other thumb under metatarsals two through five. The patient then plantarflexes the foot. If more force exists under the first metatarsal, a peroneus longus overdrive exists.¹¹ Assessment of the Achilles mechanism is fundamental to the cavus foot evaluation. Perform a Silfverskiold test to isolate gastrocnemius tightness from the soleus.¹²

A Closer Look At Biomechanical Considerations
Contrary to common thought, lengthening of the gastrocnemius soleus muscle group theoretically accentuates a cavus deformity. A tight gastrocnemius along with a plantarflexed first ray are central to the subtle cavus deformity.⁵ With the first metatarsal in a plantarflexed position, the medial forefoot strikes first with forefoot loading at 10 percent of the stance phase.This forces the subtalar joint into supination and the heel subsequently goes into varus. This is known as the tripod effect. The foot is then unable to evert at the subtalar joint and dissipate energy. The deformity, which is initially flexible, will become stiff and then rigid. As this occurs, the forefoot becomes fixed in a pronated position (valgus) and the rearfoot becomes fixed in a supinated (varus) position.

A tight gastocneumius also significantly contributes to the cavus posture. The pronated or plantarflexed forefoot creates a functional forefoot equinus that also affects ankle dorsiflexion. The weightbearing plane of the foot is more plantarflexed because the first metatarsal head is lower than the heel. With the ankle now plantarflexed, the peroneus longus develops a mechanical advantage to plantarflex the first ray, overpowering the tibialis anterior muscle. This chronic muscle imbalance leads to a progressive worsening of the foot deformity.¹³

What Radiographs Can Reveal
Radiographic evaluation shows consistent abnormalities associated with subtle cavus foot deformity.¹⁴ The lateral view shows Meary’s angle (bisection of the talus and first metatarsal) intersecting at the first metatarsal-cuneiform joint. This is due to the plantarflexion of the first metatarsal.

The high arch is signified by the measured distance between the inferior medial cuneiform and the inferior fifth metatarsal base.^14,15 The fibula is posteriorly positioned secondary to external rotation of the ankle axis.¹⁶ An increased calcaneal inclination angle is present despite a contracture of the Achilles tendon.³ The dorsal-plantar radiographic view shows a normal or decreased talocalcaneal angle. Forefoot adductus and metatarsus adductus may also be present.  

What You Should Know About Associated Clinical Pathology
Many clinical conditions are associated with the subtle cavus foot condition, which often goes unrecognized. This failure will often lead to treatment failures. Forefoot pathology can be evident in first and fifth metatarsal head lesions, and callosity formation over the styloid process of the fifth metatarsal base. Jones fracture of the fifth metatarsal base and stress fractures of metatarsals four and five are secondary to lateral overload.

Other associated stress fracture conditions may involve the tibial shafts, fibular shafts, navicular and medial malleolus.³ Tightness of the plantar fascia and Achilles tendon leads to inflammation of these structures.¹⁶ This foot type is also very prone to peroneal tendon pathology leading to tenosynovitis, subluxation, split tears and dislocation. Ankle instability and recurrent ankle sprain are common conditions associated with the subtle cavus foot.³

Pertinent Pointers On Treatment Options
The use of physical therapy involves gastrocnemius and Achilles stretching exercises. Peroneal strengthening and proprioceptive balance beam exercises may be of limited benefit.

Orthotic treatment may often be helpful but must be of specific design.^17,18 The orthotic would need to include an elevated heel to cushion and accommodate the tight gastrocnemius muscle. A cut out for the first metatarsal head can accommodate the first metatarsal’s plantarflexed position. It also allows for some eversion of the heel if the deformity is still flexible. Add a forefoot valgus wedge (metatarsals two through five) to accommodate the pronated forefoot position. Mold arch height to the arch if the subtalar joint is rigid but reduce it if there is some flexibility and pronation is available.⁴
One can address associated conditions such as ankle instability, peroneal tendon pathology and fractures at the time of cavus foot reconstruction. In early cases in which the foot remains flexible, the Coleman block test allows one to assess whether the forefoot overdrive is present. If the heel varus completely reduces with the first metatarsal dropped off the block, then address the plantarflexed first metatarsal position solely with a dorsiflexory wedge osteotomy. A gastrocnemius contracture is rare in the flexible/supinated foot.

In the more fixed or rigid cavus foot, the gastrocnemius is contracted in most cases. Determine this by the Silfverskiold test. Perform a Strayer type gastroc recession. The incision is medial and 15 cm proximal to the top of the medial malleolus.¹² Proceed to address the rearfoot varus. Using a preoperative Coleman block test enables you to determine that the rearfoot is fixed when the first metatarsal drops off the block. In this case, perform a Dwyer type calcaneal osteotomy or lateral displacement calcaneal osteotomy with a 5 mm to 10 mm lateral shift of the heel. One can use two 4.5 mm cannulated screws for fixation.  

Following correction of the equinus and heel varus deformity, examine the forefoot. If there is no residual forefoot deformity where the first ray is reduced to the level of metatarsals two through four, no further treatment is warranted. If the residual first ray deformity persists, indicating peroneal overdrive, then perform a peroneal longus to peroneal brevis transfer. Make the incision laterally at the cuboid notch. Then transfer the peroneus longus to the peroneus brevis through a longitudinal tendon incision. Pull this through plantar to dorsal via the Pulvertaft technique. If continued residual plantarflexion of the first ray persists, do a dorsiflexory wedge osteotomy of the first metatarsal or a first metatarsal-cuneiform arthrodesis, bringing it to the level of metatarsals two through five and the heel.¹⁹

Case Study: When A Jones Fracture Is Associated With Cavus Deformity
A 32-year-old Caucasian male was in the process of remodeling his basement. He was on a ladder and went up on his toes to work on the ceiling. The patient felt a “pop” with sudden pain over the lateral aspect of his left foot and was subsequently unable to bear weight on his foot. He then went to the emergency room for evaluation.

The patient’s past medical history was significant for hypertension and hyperlipidemia. Current medications included atorvastatin (Lipitor, Pfizer) and lisinopril (Prinivil, Merck). He was otherwise healthy with a height of 6 feet and weight of 289 pounds.

In the emergency room, the patient presented with a left swollen foot that was ecchymotic. There was severe tenderness on palpation to the fifth metatarsal base. Radiographic findings revealed a Jones fracture at the fifth metatarsal base with associated cavus deformity of the left foot. The clinical exam noted a peek-a-boo heel sign. The Coleman block test revealed a fixed heel varus. Radiographs showed Meary’s bisection at the first metatarsal-cuneiform joint.

The initial operative approach was open reduction and internal fixation of the fifth metatarsal left foot with an intramedullary screw, a Dwyer calcaneal osteotomy, and a first metatarsal-medial cuneiform arthrodesis. Three months postoperatively, the patient developed a non-union at the first metatarsal-medial cuneiform arthrodesis site. This non-union required revisional surgery with a reconstruction plate.

The case ultimately went to litigation. The plaintiff’s attorney supported the position that only the Jones fracture needed surgery, not the cavus reconstruction. The defense attorney supported the position of reconstruction of the cavus foot in conjunction with open reduction and internal fixation of the Jones fracture. The jury sided with the defense.

In Conclusion
The subtle cavus foot deformity is not a commonly recognized clinical entity, certainly not in comparison to pes planovalgus deformity. While the incidence of the subtle cavus foot deformity has not been described in the literature, it is not as uncommon as we thought.¹⁹ This persistent non-neurologic cavovarus foot can lead to a host of lateral overload clinical conditions. Chronic lateral ankle instability, peroneal tendinopathy and lateral column overload with recurrent stress fractures are common.^4-7,18 Recognition of this condition is paramount for conservative and surgical management of these conditions. Checking for the peek-a-boo heel sign can be a simple and sensitive clinical test to diagnose this deformity.

Dr. Visser is the Director of the Mineral Area Regional Medical Center Residency Program in Farmington, Mo., and the Director of SSM DePaul Residency Program in St. Louis.

Dr. Ansari is a third-year resident at Mineral Area Regional Medical Center in Farmington, Mo.

Dr. Thompson is a third-year resident at SSM DePaul Health Center in St. Louis.

References

1.     Chilvers M, Manoli A 2nd. Subtle cavus foot and association with ankle instability and lateral foot overload. Foot Ankle Clin. 2008; 13(2):315-324.
2.     Solis G, Hennessy MS, Saxby TS. Pes cavus: a review. Foot Ankle Surg. 2000; 6(3):145-153.
3.     Desai SN, Grierson R, Manoli A 2nd. The cavus foot in athletes: Fundamentals of examination and treatment. Oper Tech Sports Med. 2010; 18(1):27-33.
4.     Manoli A 2nd, Graham BG. The subtle cavus, foot: “the underpronator.” Foot Ankle Int. 2005; 26(3):256-63. Review.
5.     Mosca VS. The cavus foot. J Pediatr Orthop. 2001; 21(4):423-424.
6.     Fortin PT, Guettler JH, Manoli A 2nd. Idiopathic cavovarus foot and lateral ankle instability: recognition an treatment implications relating to ankle arthritis. Foot Ankle Int. 2002; 23(11):1031-7.
7.     Vienne P, Achoniger R, Helmy N, Espinosa N. Hindfoot instability in cavovarus deformity: static and dynamic balancing. Foot Ankle Int. 2007; 28(1):96-102.
8.     Johnson KA, Strom DE. Tibialis posterior tendon dysfunction. Clin Orthop. 1989; 239:196-206.
9.     Manoli A 2nd, Smith DG, Hansen ST Jr. Scarred muscle excision for the treatment of established ischemic contracture of the lower extremity. Clin Orthop. 1993; 292:309-314.
10.     Manoli A 2nd, Beals TC, Hansen ST Jr. Technical factors in hindfoot arthrodesis. Instr Course Lect. 1997; 46:347-356.
11.     Coleman SS, Chesnut WJ. A simple test for hindfoot flexibility in the cavovarus foot. Clin Orthop. 1977; 123:60-62.
12.     DiGiovanni CW, Kuo R, Tejwani N. Isolated gastrocnemius tightness. J Bone Joint Surg Am. 2002; 84-A(6):962-70.
13.     Silver RL, de la Garza J, Rang M. The myth of muscle balance. A study of relative strengths and excursions of normal muscles about the foot and ankle. J Bone Joint Surg Br. 1985; 67(3):432-437.
14.     Chada H, Pomeroy GC, Manoli A 2nd. Radiologic signs of unilateral pes planus. Foot Ankle Int. 1997; 18(9):603-604.
15.     Faciszewski T, Burks RT, Manaster BJ. Subtle injuries of the Lisfranc joint. J Bone Joint Surg Am. 1990; 72(10):1519-1522.
16.     Lloyd-Roberts GC, Swann M, Catterall A. Medial rotation osteotomy for severe residual deformity in clubfoot. A preliminary report on a new method of treatment. J Bone Joint Surg Br. 1974; 56(1):37-43.
17.     Bordelon RL. Orthotics, shoes, and braces. Orthop Clin North Am. 1989; 20(4):751-757.
18.     Bordelon RL. Practical guide to foot orthoses. J Musculoskel Med. 1989; 6(1):71-87.
19.     Maskill MP, Maskill JD, Pomeroy GC. Surgical management and treatment algorithm for the subtle cavovarus foot. Foot Ankle Int. 2010; 31(12):1057-1063.